THE LIVING PRINCIPLE IN PLANTS. 
1, PROTOPLASTS CONSIDERED AS THE SEAT OF LIFE. 
Discovery of the Cell.—Discovery of Protoplasm. 
DISCOVERY OF THE CELL. 
What is life? This ever-interesting question has seemed to approach nearer 
solution on the occasion of every great scientific discovery. But never did the hope 
of being able to penetrate the great secret of life appear better founded than at the 
time when, among other memorable developments of science, it was discovered that 
objects could be rendered visible on an enlarged scale by the use of glass lenses, and 
the microscope was invented. These magnifying glasses were expected to yield, 
not only an insight into the minute structure of living beings which is invisible to 
the naked eye, but also revelations concerning the processes which constitute life 
in plants and animals. The first discoveries made with the microscope, between 
1665 and 1700, produced a profound impression on the observers. The Dutch 
philosopher Swammerdam became almost insane at the marvels revealed by his 
lenses, and at last destroyed his notes, having come to the conclusion that it was 
sacrilege to unveil, and thereby profane, what was designed by the Creator to remain 
hidden from human ken. The observations of Leeuwenhoek (1632-1723) with 
magnifying glasses formed by melting fine glass threads in a lamp, were for a 
long time held to be delusions; and it was not till the English observer Robert 
Hooke had confirmed the fact of the existence of the minute organisms seen by 
Leeuwenhoek in infusions of pepper, and had exhibited them under his microscope 
in 1667 at a meeting of the Royal Society in London, that doubts as to their actual 
existence disappeared. Indeed a special document was then drawn up and signed 
by all those who were satisfied, on the evidence of their own eyesight, of the accu- 
racy of the observation; and this clearly shows how greatly people were impressed 
with the importance of these discoveries. Of the different forms of the tiny 
organisms, amounting to nearly four hundred, which were at that time distinguished, 
and all included under the name Infusoria, because first seen in infusions of pepper- 
corns, some only are at the present day reckoned as animals. In many cases it 
has been ascertained that they are the spores of plants, whilst others again belong 
to the boundary-land where the animal and vegetable kingdoms are merged. 
The presence or absence of movement used to be considered as the most decisive 
mark of the difference between animals and plants, and, accordingly, all the minute 
